Light scattering polymeric masses

ABSTRACT

MIXTURES OF A PARAFFIN SUCH AS DOCOSANE IN A POLYMER SUCH AS ETHYL METHACRYLATE ARE PRODUCED BY ADMIXING THE PARAFFIN IN A MONOMER OF THE POLYMER AND THEN POLYMERIZING THE MONOMER CONVENTIONAL POLYMERIZATION TECHNIQUES THE RESULT IS AN INTIMATE MIXTURE OF MICROSCOPIC DOMAINS OF THE PARAFFIN IN THE POLYMER, THE PARAFFIN POLYMER MIXTURES HAVE A WIDE VARIETY OF USES, E.G.M THEY CAN BE EMPLOYED AS THE IMAGE PORTION (SCREEN) OF CONVENTIONAL DISPLAY DEVICES.

United States Patent 3,832,315 LIGHT SCATTERING POLYMERIC MASSESFrederick J. Bueche, Dayton, Ohio, assignor to The National CashRegister Company, Dayton, Ohio No Drawing. Filed Feb. 1, 1971, Ser. No.111,735

Int. Cl. C08f 45/52 U.S. Cl. 260-285 R 10 Claims ABSTRACT OF THEDISCLOSURE Mixtures of a parafiin such as docosane in a polymer such asethyl methacrylate are produced by admixing the parafiin in a monomer ofthe polymer and then polymerizing the monomer by conventionalpolymerization techniques. The result is an intimate mixture ofmicroscopic domains of the parafiin in the polymer. The paraffin polymermixtures have a wide variety of uses, e.g., they can be employed as theimage portion (screen) of conventional display devices.

This invention relates to a process for the production ofparaffin-polymer pairs, to the products thereby produced and to displaydevices.

The two materials of this invention have been selected to exhibitapparent mutual immiscibility and yield a hazy, translucent oropalescent body over a certain temperature range which contains anintimate mixture of microscopic domains of the parafiin in the polymer.While the parafi'in-polymer pairs are hereinafter referred to as a body,film or sheet, it should be understood that these terms are employed forthe convenience of verbal de scription only and should not be construedto limit the invention unduly. The physical properties of the body varywidely with temperature depending on the melting point of the parafiin,i.e., depending on whether or not the parafiin is in a crystalline ormolten state. It is preferred that the paraffin be crystalline forscreens, i.e., just above the use temperature. Below the melting pointof the wax the body is highly translucent, due to the presence ofdispersed crystalline paraffin particles in the polymer. At or above themelting point of the paraffin, the body becomes optically clear. It isbelieved that the wax melts to form a liquid when then dissolves in thepolymer.

Various processes for the production of translucent polymeric materialand the resulting products are known in the art. For example, see U.S.Pat. 2,320,924 which discloses translucent sheets of polymers of styreneand methyl methacrylate. Other prior art includes United States PatentApplication Ser. No. 836,021, filed June 24, 1969, in the name ofAntoinette M. Purcell, Curt Thies, Morris I. Bank and James W.Lefiingwell and assigned to the assignee herein. In some of these priorart materials, the amount of polymer determines the degree oftranslucency, while in other materials the degree of translucencydepends upon the employment of a solvent.

It now has been found that translucent or transparent bodies can beproduced by dissolving a parafiin in a monomer and polymerizing themonomer by conventional methods. The resulting body is a uniformdispersion of microscopic domains of the paraffin in the polymet. Theparaffin is essentially completely miscible with the polymer above thecrystal-melting point of the paraffin but essentially completelyimmiscible with the resulting polymer at or just below the melting pointof the paraffin.

Accordingly, an object of this invention is to provide a process for theproduction of mixtures of a paraffin in a polymer.

Another object of this invention is to provide mixtures of paraffin in apolymer.

Patented Aug. 27, 1974 ice Still another object of this invention is toprovide display devices.

Other objects, aspects and advantages of this invention will be apparentto one skilled in the art from the following disclosure and appendedclaims.

The paraffins that are employed in this invention are alkanes orsaturated aliphatic hydrocarbons. These paraffins can be amino (NHcarboxyl (COOH), or hydroxyl (-O'H) substituted in the alpha or betaposition. These waxes are represented by the formula wherein R is analkyl radical having '9 to 35 carbon atoms, X is hydrogen or an amino(NH carboxyl (COOH), or hydroxyl (OH) radical. Preferably, R is an alkylradical having 12 to 24 carbon atoms and X is hydrogen. Specificexamples of these paraffins are docosane, docosoic acid, docosyl alcoholand docosyl amine. Other examples are decane, decyclic acid, decylalcohol and decyl amine. For the sake of clarity, other representativeparafiins are not being listed as they can be explicitly derived fromthe above description. Further, representative parafiins can be readilyobtained from the Handbook 07 Chemistry and Physics, Forty-SixthEdition, published by The Chemical Rubber Company, Cleveland, Ohio.

The monomers that are employed in this invention are styrene, butadiene,methyl methacrylate, ethyl methacrylate, butyl methacrylate and thelike, and mixtures thereof, preferably the methacrylates.

The ratio of paraffin to monomer can vary widely. Generally, a majorportion of monomer and a minor portion of paraffin are employed.Preferably, up to 20 weight percent of the parafiin is employed.

The polymerization of this invention can be carried out underconventional polymerization conditions. Generally, the polymerization iscarried out at a tempera-ture ranging up to 150 degrees centigrade, at apressure ranging up to 500 atmospheres and for a time ranging up to 3days. Preferably, the polymerization is carried out at a temperatureranging from 50 degrees to degrees centigrade, at atmospheric pressureand for a time ranging up to 48 hours. Other polymerization conditionswhich can be employed in this invention are disclosed in previouslymentioned U.S. Pat. 2,320,924. The polymerization can be carried outwith or without initiators or cross-linking agents such as ethylenedi(methacrylate); however, the polymerization always is carried out inthe absence of a conventional solvent. While the parafiin is misciblewith the monomer, the paratlin is immiscible with the resulting polymerbelow the crystal melt temperature of the parafiin.

A film, once prepared from the paraffin-polymer pairs of this inventioncan be employed in conventional display devices as the imaging portion,i.e., the face or screen. The performance of these screens depends uponthe two-phase dispersion of the paratfin in the polymer, i.e., upon theimmiscibility of the paraffin in the polymer. Below the melting point ofthe paraffin, the film is highly translucent due to crystallineproperties of the paraffin dispersed in the polymer. The translucencydepends upon the light scattering properties of the paraffin. This filmis an intimate mixture of microscopic domains of the paraffin in thepolymer. Due to the fine dispersion of the paraffin in the polymer, thefilm exhibits uniform light scattering properties. The paraffin-polymermixtures of this invention also can be used in any films, coatings ormolded products. Specific examples are sky-lights and a wide variety ofwindow panes such as those used in greenhouses. If an optically clearfilm is required, the temperature of the display device is at or abovethe melting point of the parafiin. The thickness of the films can varywidely. Generally, the thickness can range up to 1 millimeter,preferably 5 to mils.

The film possesses a grain-free translucent optical property. Generally,the radius of the microscopic domains of the paraffin range from 100 to500 Angstroms (A.), preferably 200 to 400 A.

The advantages of this invention are further illustrated by thefollowing examples. The reactants and the proportions and other specificconditions are presented as being typical and should not be construed tolimit the invention unduly.

EXAMPLE I The materials employed herein consist of two phases. They wereprepared by dissolving 3.3 weight percent docosane in a monomer of ethylmethacrylate. After sealing the materials in a test tube, the monomerwas polymerized without an initiator at a temperature of 85 degreescentigrade initially for 24 hours and finished oiT at increasingtemperatures up to 130 degrees centigrade for 24 hours. The phaseseparation occurs during polymerization at late stages in the process. Aminimum concentration of 0.2 weight percent of docosane was exceeded forphase separation to occur.

To use the sample for scattering measurements, the solid body wasmachined into 1 cm. diameter discs with a thickness of l millimeter.Sample surfaces were polished and most of the discs were furthersmoothed by heating between glass plates. All scattering measurementswere made in a modified Brice-Pheonix light scattering instrument 4358to 5461 A. wavelengths. The discs were mounted freely in the light pathof the instrument, which was a beam about 2 millimeters square. Aftercorrection for refraction at the disc surface, the minimum scatteringangle was considerably less than 5 degrees. The domain radius fordocosane in this Example average 340 A.

EXAMPLE II The materials employed herein consist of two phases. Theywere prepared by dissolving 10.0 weight percent, of a paraffin in amonomer of butyl methacrylate. Paraffins having 20, 22, 24, 26, 28, 32and 36 carbon atoms were employed. After sealing the pairs of materialsin test tubes, the monomers were polymerized without an initiator at atemperature of 90 degrees centigrade initially for approximately 15hours. Although no initiator was employed, the resulting samples wererinsed with 10 percent sodium hydroxide-water solution, followed bywater to remove any free radical inhibitor present. All but the C massremained clear through the polymerization process. The C sample wasopalescent.

To use the samples for light scattering measurements, differentialscanning calorimetric measurements, thermomechanical analysis anddielectric relaxation measurements, the resulting solid masses werepressed between polished aluminum plates, heated to about 150 degreescentigrade and quenched in cold water. The resulting sheet had athickness of about mils.

EXAMPLE III The sheets of Example II were subjected to thermal treatmentas in a diiferential scanning calorimeter. It was found that the sheetsundergo a transformation from a white opalescent state to a visuallyclear state when the temperature of the sheet rises above thecrystalline melting point of the incorporated parafiin. Upon cooling,the sheet returns to the opalescent state when the temperature of thesheet drops below the crystalline melting point of the incorporatedparafiin. This process is reversible and can be repeated many times.However, the temperature of recrystallization often occurs 10 degrees todegrees centigrade below the paraffins melting temperature due to themolten paraffins tendency to supercool before recrystallizing. Themelting and crystallization process can be readily followed bydifferential scanning calorimetric measurements, dielectric relaxationmeasurement, or thermal mechanical analysis.

EXAMPLE IV Samples of the sheets prepared in Example II were employed asviewing screens for rear view projectors. The compositions of the sheetswere as follows: 1 gram of paraffin and 5 mililiters of butylmethacrylate; 1 gram of parafiin and 10 milliliters of butylmethacrylate; and 1 gram of paraffin and 20 milliliters of butylmethacrylate. C and C paraffins were employed in each sample. The lightscattering of the sheets was determined with a device having a 550 mlight source, a photocell detector and a sample holder. The relativelight intensity transmitted through the sheet then was measured as afunction of the viewing angle. All measurements were taken below themelting point of the paraffin. The results demonstrated that scatteringwas dependent upon the weight percent of paraffin present. Higherparafiin content resulted in light scattering being less dependent uponthe viewing angle. Sheet thickness of the C sheet was varied from 5 to15 mils and it was observed that less angle dependence occured as filmthickness increased. However, all the sheets employed were visuallygrain free, thereby indicating small scattering centers of the paraffinthroughout the polymer.

EXAMPLE V The sheets prepared in Example II and subjected to thermaltreatment as in Example III can be used for writing or printingpurposes. A source of energy such as a print head, electron beam orlaser ray can cause a selected area of the sheet to become clear uponheating. The writing or printing is normally the clear area; however,the opposite effect can be had by heating the background instead of thewriting. This thermally treated material can be used to form aprojection device as the heated area of the sheet allows the passage oflight, while the cooler area scatters light readily.

Although this invention has been described in considerable detail, itmust be understood that such detail is for the purpose of illustrationonly and that many variations and modifications can be made by oneskilled in the art without departing from the scope and spirit thereof.

What is claimed is:

1. A process for producing an intimate mixture of microscopic domains ofa paraffin in a polymer which comprises the steps of (a) dissolving aparaflin represented by the formula wherein R is an alkyl radical having9 to 35 carbon atoms and X is hydrogen or an amino, carboxyl or hydroxylradical in a monomer of styrene, butadiene, methyl methacrylate, ethylmethacrylate, butyl methacrylate or mixtures thereof, and

(b) subjecting the resulting solution to polymerization conditions untilpolymerization of the monomer is complete.

2. A process according to claim 1 wherein a minor portion of theparafiin and a major portion of the monomer are employed, based on thetotal weight of the mixture.

3. A process according to claim 1 wherein the paraffin comprises up to20 weight percent of the mixture.

4. A process according to claim 1 wherein R is an an alkyl radicalhaving 12 to 24 carbon atoms, X is hydrogen and the monomer is methylmethacrylate, ethyl methacrylate, ethyl methacrylate or butylmethacrylate.

5. A process according to claim 1 wherein the paraffin is docosane, themonomer is ethtyl methacryalte and docosane comprises 3.3 weight percentof the mixture.

6. An intimate mixture of microscopic domains of a minor portion of aparaffin represented by the formula wherein R is an alkyl radical having9 to 35 carbon atoms and X is hydrogen or an amino, carboxyl or hydroxylradical in a major portion of a polymer of poly(styrene),poly(butadiene), poly(methyl methacrylate), poly(ethyl methacrylate),poly(butyl methacrylate) or copolymers thereof, wherein the radius ofthe domains of the parafiin range from 100 to 500 A.

7. A mixture according to claim 6 wherein R is an alkyl radical having12 to 24 carbon atoms, X is hydrogen and the polymer ispoly(methy1methaerylate), poly(ethyl methacrylate) or poly(buty1methacrylate).

8. A mixture according to claim 6 wherein the radius of the domains ofthe paraffin ranges from 200 to 400 A.

9. A mixture according to claim 6 wherein the paraflin comprises up to20 weight percent of the mixture.

10. A mixture according to claim 6 wherein the paraf- 6 fin is docosane,the polymer is poly(ethyl methacrylate), the average radius of thedomains of the wax is 340 A., and the paraffin comprises 3.3 weightpercent of the mixture.

References Cited UNITED STATES PATENTS 2,320,924 5/1939 Gift 2608853,324,074 6/1967 McManimie 26041 3,412,059 11/1968 Stickelmeyer et a1.26028.5

MORRIS LIEBMAN, Primary Examiner S. L. FOX, Assistant Examiner US. Cl.X.R. 26028.5 A, 28.5 B

